Coherent control of enhanced second-harmonic generation in a plasmonic nanocircuit using a transition metal dichalcogenide monolayer.

Nonlinear nanophotonic circuits, renowned for their compact form and integration capabilities, hold potential for advancing high-capacity optical signal processing. However, limited practicality arises from low nonlinear conversion efficiency. Transition metal dichalcogenides (TMDs) could present a promising avenue to address this challenge, given their superior optical nonlinear characteristics and compatibility with diverse device platforms. Nevertheless, this potential remains largely unexplored, with current endeavors predominantly focusing on the demonstration of TMDs' coherent nonlinear signals via free-space excitation and collection. In this work, we perform direct integration of TMDs onto a plasmonic nanocircuitry. By controlling the polarization angle of the input laser, we show selective routing of second-harmonic generation (SHG) signals from a MoSe2 monolayer within the plasmonic circuit. Routing extinction ratios of 14.86 dB are achieved, demonstrating good coherence preservation in this hybrid nanocircuit. Additionally, our characterization indicates that the integration of TMDs leads to a 13.8-fold SHG enhancement, compared with the pristine nonlinear plasmonic nanocircuitry. These distinct features-efficient SHG generation, coupling, and controllable routing-suggest that our hybrid TMD-plasmonic nanocircuitry could find immediate applications including on-chip optical frequency conversion, selective routing, switching, logic operations, as well as quantum operations.

Near-Field Photodetection in Direction Tunable Surface Plasmon Polaritons Waveguides Embedded with Graphene.

2D materials have manifested themselves as key components toward compact integrated circuits. Because of their capability to circumvent the diffraction limit, light manipulation using surface plasmon polaritons (SPPs) is highly-valued. In this study, plasmonic photodetection using graphene as a 2D material is investigated. Non-scattering near-field detection of SPPs is implemented via monolayer graphene stacked under an SPP waveguide with a symmetric antenna. Energy conversion between radiation power and electrical signals is utilized for the photovoltaic and photoconductive processes of the gold-graphene interface and biased electrodes, measuring a maximum photoresponsivity of 29.2 mA W-1 . The generated photocurrent is altered under the polarization state of the input light, producing a 400% contrast between the maximum and minimum signals. This result is universally applicable to all on-chip optoelectronic circuits.

Plasmonic topological quasiparticle on the nanometre and femtosecond scales.

At the interface of classical and quantum physics, the Maxwell and Schrödinger equations describe how optical fields drive and control electronic phenomena to enable lightwave electronics at terahertz or petahertz frequencies and on ultrasmall scales1-5. The electric field of light striking a metal interacts with electrons and generates light-matter quasiparticles, such as excitons6 or plasmons7, on an attosecond timescale. Here we create and image a quasiparticle of topological plasmonic spin texture in a structured silver film. The spin angular momentum components of linearly polarized light interacting with an Archimedean coupling structure with a designed geometric phase generate plasmonic waves with different orbital angular momenta. These plasmonic fields undergo spin-orbit interaction and their superposition generates an array of plasmonic vortices. Three of these vortices can form spin textures that carry non-trivial topological charge8 resembling magnetic meron quasiparticles9. These spin textures are localized within a half-wavelength of light, and exist on the timescale of the plasmonic field. We use ultrafast nonlinear coherent photoelectron microscopy to generate attosecond videos of the spatial evolution of the vortex fields; electromagnetic simulations and analytic theory confirm the presence of plasmonic meron quasiparticles. The quasiparticles form a chiral field, which breaks the time-reversal symmetry on a nanometre spatial scale and a 20-femtosecond timescale (the 'nano-femto scale'). This transient creation of non-trivial spin angular momentum topology pertains to cosmological structure creation and topological phase transitions in quantum matter10-12, and may transduce quantum information on the nano-femto scale13,14.

A Polarization-Actuated Plasmonic Circulator.

A circulator for surface plasmon polaritons (SPPs) based on a plasmonic two-wire transmission-line (TWTL) structure is experimentally realized. A TWTL offers two distinct plasmon modes that can be independently excited, solely determined by the polarization of the laser field. Through controlled superposition of the two modes, TWTLs are exploited to enable polarization-actuated plasmonic circulators. In the first demonstration, the coupling antennas to the plasmonic circulator are designed to circulate SPPs sensitive to linearly polarized excitation. In the second design, the circulator reacts to the spin angular momenta carried by circularly polarized laser excitations. In both cases, the SPP circulation directions are directly controlled by the laser polarization, and the number of ports is easily expandable. Experimentally, a wide optical operational bandwidth of ∼100 nm is achieved. The results show a major step toward the realization of multifunctioning photonic nanocircuitry.

Modal Symmetry Controlled Second-Harmonic Generation by Propagating Plasmons.

A new concept for second-harmonic generation (SHG) in an optical nanocircuit is proposed. We demonstrate both theoretically and experimentally that the symmetry of an optical mode alone is sufficient to allow SHG even in centro-symmetric structures made of centro-symmetric material. The concept is realized using a plasmonic two-wire transmission-line (TWTL), which simultaneously supports a symmetric and an antisymmetric mode. We first confirm that emission of second-harmonic light into the symmetric mode of the waveguide is symmetry-allowed when the fundamental excited waveguide modes are either purely symmetric or antisymmetric. We further switch the emission into the antisymmetric mode when a controlled mixture of the fundamental modes is excited simultaneously. Our results open up a new degree of freedom into the designs of nonlinear optical components and should pave a new avenue toward multifunctional nanophotonic circuitry.

Investigation of temporal Talbot operation in a conventional optical tapped delay line structure.

We propose a novel scheme of temporal Talbot effect achieving optical pulse train repetition-rate multiplication in a conventional tapped delay line structure. While it is generally used for spectral amplitude filtering, we show that such architecture could also be configured for spectral phase-only filtering, as well as for a combination of amplitude and phase filtering regimes. We theoretically derive and numerically simulate the working principle of the concept, followed by a proof-of-principle experimental demonstration using an off-the-shelf Mach-Zehnder delay line interferometer, which corresponds to the simplest version of the proposed structure. We address the efficiency, and potential performance degradation in the presence of power imbalance and delay line length inaccuracy of the architecture, together with applied phase error.

Talbot effect on orbital angular momentum beams: azimuthal intensity repetition-rate multiplication.

We propose and experimentally demonstrate the azimuthal Talbot effect on orbital angular momentum (OAM) beams. By applying predetermined phases to a number of OAM beams carrying different topological charges, the intensity petal is self-imaged in the azimuthal angle, with arbitrary azimuthal repetition-rate multiplication. The close analogy between temporal and azimuthal Talbot self-imaging is studied. In addition, the effect of amplitude apodization of the OAM spectrum on the resulting intensity pattern, and the azimuthal Talbot effect on Laguerre-Gaussian beams of the same radial indices, are experimentally investigated. All of our experimental images are in excellent agreement with simulation results.

Large-scale and structure-tunable laser spectral compression in an optical dispersion-increasing fiber.

Laser spectral compression by a factor of 102.8 is experimentally achieved through optical soliton propagation in a dispersion-increasing fiber. By varying the input pulse energy, the wavelength tuning range of the compressed spectral peak could exceed 115 nm. Spectrally compressed spectrum with two bright peaks is demonstrated for the first time, to our knowledge. The structure of the dual-peaked compressed spectra is adjustable through the interplay of initial pulse chirp and energy. All of the experimental data are compared to numerical results and are found in good agreement.

Creating optical near-field orbital angular momentum in a gold metasurface.

Nanocavities inscribed in a gold thin film are optimized and designed to form a metasurface. We demonstrate both numerically and experimentally the creation of surface plasmon (SP) vortex carrying orbital angular momentum in the metasurface under linearly polarized optical excitation that carries no optical angular momentum. Moreover, depending on the orientation of the exciting linearly polarized light, we show that the metasurface is capable of providing dynamic switching between SP vortex formation or SP subwavelength focusing. The resulting SP intensities are experimentally measured using a near-field scanning optical microscope and are found in excellent quantitative agreements as compared to the numerical results.

Mode conversion in high-definition plasmonic optical nanocircuits.

Symmetric and antisymmetric guided modes on a plasmonic two-wire transmission line have distinct properties and are suitable for different circuit functions. Being able to locally convert the guided modes is important for realizing multifunctional optical nanocircuits. Here, we experimentally demonstrate successful local conversion between the symmetric and the antisymmetric modes in a single-crystalline gold plasmonic nanocircuit with an optimally designed mode converter for optical signals at 194.2 THz. Mode conversion may find applications in controlling nanoscale light-matter interaction.

Self-referenced frequency comb measurement by using a polarization line-by-line pulse shaper.

A polarization line-by-line pulse shaper is used for generation and noniterative spectral phase retrieval of optical arbitrary waveforms (OAWs) spanning over the entire repetition period. The method is completely reference-free, making it particularly attractive in measuring high repetition-rate OAW.

Adiabatic pulse propagation in a dispersion-increasing fiber for spectral compression exceeding the fiber dispersion ratio limitation.

Adiabatic soliton spectral compression in a dispersion-increasing fiber (DIF) with a linear dispersion ramp is studied both numerically and experimentally. The anticipated maximum spectral compression ratio (SCR) would be limited by the ratio of the DIF output to the input dispersion values. However, our numerical analyses indicate that SCR greater than the DIF dispersion ratio is feasible, provided the input pulse duration is shorter than a threshold value along with adequate pulse energy control. Experimentally, a SCR of 28.6 is achieved in a 1 km DIF with a dispersion ratio of 22.5.

Selective trapping or rotation of isotropic dielectric microparticles by optical near field in a plasmonic archimedes spiral.

We demonstrate selective trapping or rotation of optically isotropic dielectric microparticles by plasmonic near field in a single gold plasmonic Archimedes spiral. Depending on the handedness of circularly polarized excitation, plasmonic near fields can be selectively engineered into either a focusing spot for particle trapping or a plasmonic vortex for particle rotation. Our design provides a simple solution for subwavelength optical manipulation and may find applications in micromechanical and microfluidic systems.

Multimode plasmon excitation and in situ analysis in top-down fabricated nanocircuits.

We experimentally demonstrate synthesis and in situ analysis of multimode plasmonic excitations in two-wire transmission lines supporting a symmetric and an antisymmetric eigenmode. To this end we irradiate an incoupling antenna with a diffraction-limited excitation spot exploiting a polarization- and position-dependent excitation efficiency. Modal analysis is performed by recording the far-field emission of two mode-specific spatially separated emission spots at the far end of the transmission line. To illustrate the power of the approach we selectively determine the group velocities of symmetric and antisymmetric contributions of a multimode ultrafast plasmon pulse.

Noniterative data inversion of phase retrieval by omega oscillating filtering for optical arbitrary waveform measurement.

We propose a noniterative data inversion process for the phase retrieval by omega oscillating filtering method that could measure both isolated attosecond pulses and periodic optical arbitrary waveform (OAW). The built-in phase modulation depth recovery not only prevents the need of independent calibration (a critical advantage in the extreme ultraviolet regime) but provides a self-consistency check for the data integrity. Our experiments successfully retrieved OAW with ~100% duty cycle in the near infrared regime.

Polarization line-by-line pulse shaping for the implementation of vectorial temporal Talbot effect.

Vectorial optical arbitrary waveform generation is experimentally demonstrated by applying polarization line-by-line pulse shaping on a phase-modulated continuous laser frequency comb. Polarization shaped optical waveforms extending a 50-ps time window are successfully synthesized. Temporal Talbot effect is extended into the vectorial regime, where the distinct periodic temporal phases of the two orthogonally polarized pulse trains are exploited. In one example, we generate repetition-rate doubled circularly polarized pulses with alternating pulse-by-pulse handedness. In another example, complex instantaneous field polarizations are synthesized through the combination of line-by-line amplitude and temporal Talbot phase shaping. Our experimental results are measured through a dual-quadrature spectral interferometry system and are found in excellent agreements to the applied shaping controls.

Plasmonic mode converter for controlling optical impedance and nanoscale light-matter interaction.

To enable multiple functions of plasmonic nanocircuits, it is of key importance to control the propagation properties and the modal distribution of the guided optical modes such that their impedance matches to that of nearby quantum systems and desired light-matter interaction can be achieved. Here, we present efficient mode converters for manipulating guided modes on a plasmonic two-wire transmission line. The mode conversion is achieved through varying the path length, wire cross section and the surrounding index of refraction. Instead of pure optical interference, strong near-field coupling of surface plasmons results in great momentum splitting and modal profile variation. We theoretically demonstrate control over nanoantenna radiation and discuss the possibility to enhance nanoscale light-matter interaction. The proposed converter may find applications in surface plasmon amplification, index sensing and enhanced nanoscale spectroscopy.

Highly efficient femtosecond pulse stretching by tailoring cavity dispersion in erbium fiber lasers with an intracavity short-pass edge filter.

We demonstrate highly efficient pulse stretching in Er(3+)-doped femtosecond mode-locked fiber lasers by tailoring cavity dispersion using an intracavity short-pass edge filter. The cavity dispersion is preset at around zero to obtain the shortest pulsewidth. When the cutoff wavelength of the short-pass edge filter is thermo-optically tuned to overlap the constituting spectral components of mode-locked pulses, large negative waveguide dispersion is introduced by the steep cutoff slope and the total cavity dispersion is moved to normal dispersion regime to broaden the pulsewidth. The time-bandwidth product of the mode-locked pulse increases with the decreasing temperature at the optical liquid surrounding the short-pass edge filter. Pulse stretch ratio of 3.53 (623.8 fs/176.8 fs) can be efficiently achieved under a temperature variation of 4 °C.

Wavelength-tunable spectral compression in a dispersion-increasing fiber.

We demonstrate, both numerically and experimentally, adiabatic soliton spectral compression in a dispersion-increasing fiber (DIF). We show that a positively chirped pulse provides better spectral compression in a DIF with a large anomalous dispersion ramp. An experimental spectral compression ratio of 15.5 is obtained using 350 fs positively chirped input pulse centered at 1.5 µm. A 30 nm wavelength tuning ability is experimentally achieved.

Forty-photon-per-pulse spectral phase retrieval by shaper-assisted modified interferometric field autocorrelation.

We retrieve the spectral phase of 400 fs pulses at 1560 nm with 5.2 aJ coupled pulse energy (40 photons) by the modified interferometric field autocorrelation method, using a pulse shaper and a 5 cm long periodically poled lithium niobate waveguide. The carrier-envelope phase control of the shaper can reduce the fringe density of the interferometric trace and permits longer lock-in time constants, achieving a sensitivity of 2.7×10(-9) mW(2) (40 times better than the previous record for self-referenced nonlinear pulse measurement). The high stability of the pulse shaper allows for accurate and reproducible measurements of complicated spectral phases.